1. Field of the Invention
The present invention relates to a reproducing apparatus for reproducing information from a record medium such as an optical disc, a magneto-optical disc, or a video tape.
2. Description of the Related Art
In an apparatus that reads information using a relative motion between an information record medium and an information read head as in a reproducing apparatus for an optical disc, a magneto-optical disc, or a video tape, a noise referred to as a jitter takes place in a reproduced signal due to deformation of a record medium, a dislocation thereof, an irregular rotation of a driving unit that drives the record medium and a record head. Thus, since the jitter takes place due to a dislocation of a relative motion between the record medium and a deformation of the record medium, the jitter becomes strong proportional to the relative speed and the read speed of the read head.
On the other hand, as record media and reproducing apparatuses have advanced, the record densities of record media have been increased and the amount of information that can be read in a unit time has become large. However, the required amount of information such as audio information and video information reproduced on a TV display is constant per unit time. Thus, in the field of audio and video apparatuses, information can be read faster than it is used. With the speed difference, information is temporarily stored in a storing unit such as a RAM (Random Access Memory) at a high transfer rate. The information is read from the storing unit at a low transfer rate and then supplied to an audio portion and a video portion.
In the case that a storing unit is used as a buffer for information, even if the reading operation of information is temporarily stopped due to skipping of a read head or dislocation of a record medium, when the reading operation is restored before the information stored in the storing unit becomes empty, information can be successively supplied to the audio portion and the video portion, not suspended. The structure that provides an optical disc reproducing apparatus with a shock proof performance is referred to as an ESP (Electric Shock Proof) structure. The storing unit that temporarily stores information is referred to as a shock proof memory.
In the optical disc reproducing apparatus equipped with such a shock proof function, digital data is read and stored corresponding to control data recorded on an optical disc. Alternatively, the optical system is reallocated corresponding to the control data. Thus, when the control data cannot be successively read, the data cannot be accurately reproduced. Alternatively, since the data cannot be properly connected, a continuous of the audio output cannot be maintained. Thus, in the system where the control data has been recorded on a record medium such as a disc along with audio data and video data, even if the audio data and video data are correctly read, when the control data cannot be successively read, data cannot be stored in the shock proof memory.
Audio digital data is error-corrected with CIRC (Cross Interleaved Reed Solomon Code). In contrast, with respect to control data, only CRC error correction code is added. Thus, the reliability of the control data is lower than the reliability of the audio digital data. This structure is a bottleneck in the shock proof process of a disc that has a large jitter. With a disc having a large jitter, since the read level of a high frequency component (as in a read signal of short pits) is normally low, when the reproduction speed of the optical disc is increased, the S/N (Signal/Noise) ratio deteriorates due to the influence of an electric noise of the reproducing circuit. Thus, the control data cannot be correctly read.
To easily read the control code, it is necessary to decrease the reproduction speed. However, in this case, the data read speed decreases. Thus, the shock proof function deteriorates and thereby the shock proof performance decreases.